Field emission cathodes have been successfully used in high resolution electron optical devices, like scanning electron microscopy and transmission electron microscopy [1]. In these devices, the cathode consists of a single needle shape emitter with a sharp tip on the order of several tens of nanometers. Even though a cold clean cathode is electrically stable at emission densities up to 107 A·cm−2 [2], the tiny emission area limits the total emission current. Therefore, to achieve a relatively high total emission current, a field emitter array is used.
The Spindt cathode (i.e. a metal cone emitter array with individual hole gates) has been widely studied since it was first designed in 1968 [3]. Many prototypes of Spindt cathode-based electron devices have been demonstrated [4-7]; however, they are still not successfully commercialized. For example, a metal emitter has a lifetime of just a few seconds in a medium level vacuum which limits the practical application of the Spindt cathode.
On the other hand, due to a high melting temperature and a low surface diffusion, a carbon-based field emitter can operate more stably in a medium vacuum [8, 9]. Furthermore, it has been reported that Carbon NanoTube (CNT)/Carbon NanoFiber (CNF) emitters can provide a stable emission current in inert gas under atmospheric pressure [10]; however there are still some deficiencies such that CNT emitters grown on resistive materials do not function properly.